Heart failure (HF) is the leading cause of mortality and morbidity, which afflicts 5.7 million Americans. HF management includes surgery, implantable device and pharmacological therapy targeting angiotensin and adrenergic signaling. Numerous animal models of heart failure have been generated and studied for decades in effort to identify therapeutic targets for treatment of human HF patients. However, it is becoming increasingly evident that this strategy has yielded limited therapeutic options for the treatment o HF. Significant genetic, molecular, cellular, anatomical, and systemic differences among species are likely to be responsible for failure of translation from cell lines and animal models t humans. Cardiac rhythm disorders are striking examples of such translational failure. Despite deep knowledge of the biophysical properties of numerous ion channels, pumps, and exchangers gained over half a century of research conducted at huge expense, current pharmacological therapies used to treat arrhythmias are nonspecific and often ineffective. The main reason for this failure is the complexity of human cardiac physiology at the molecular, cellular and tissue levels. It is paradoxical, but we know much more about ion channels and action potentials in the mouse, rat, guinea pig, rabbit, and canine as compared to our own species - Homo sapiens. We have recently developed a program, which allows investigation of the mechanisms of arrhythmogenic remodeling in live human hearts in vitro. In this project we will investigate a number of mechanistic hypothesis linking HF and arrhythmia in live cardiac tissue from donors and patients with HF. In summary, we will develop, refine and extend experimental methodology, which is currently applied only to animal cardiac preparations in basic physiology laboratories, to deepen our understanding of human cardiac pathophysiology. This approach will modify and enhance the currently dominant translational paradigm and provide new important directions of research, which will stimulate and reinvigorate a biomedical research community that has ignored human physiology and thus delayed effective translation of needed therapies for HF and sudden cardiac death.